9 minute read

Transmissions, Gearing and RPM 

Compliments of Blacknights @ dodgeforums.com

Hey guys and gals, so in response to a thread I ended up compiling a ton of information about gearing and rpm numbers. I've tried to make it as thorough as possible, everything from transmissions to gearing ratios. If you have some information (or proofreading) that you think could be add to this master sheet, feel free to pm so I can make it even better.

Anyways, on to stuff you wanted facts!

I've divided up everything so things are easy to find and understand, if you don't know what you have, I've also taken the time to match your transmission with your engine. Automatic transmissions are first on the list, newest transmission first. With dodge the automatics are often the same or similar construction. Example 45RFE is actually a 545RFE the gearing numbers are the same, what is different is TCM (Transmission Control Module). The 4(2,4,6)RE are differentish, I'll put those in after the 545RFE so scroll farther down for those. For those bastards (I hate you out of jealousy) who have a manual 5 speed tranny NV3500 or upgraded to the NV4500, I've made you scroll past the automatics.

(5)45RFE: This transmission is matted with all 4.7 engines (and the hemi engine in other vehicles). This is actually designed and made by Chrysler itself in the US

1st- 3.00

2nd- 1.67 (With the 545RFE the kick down planetary gearing is 1.50)

3rd- 1.00

4th- 0.75

5th- 0.68 (545RFE's 5th gear, when your TCM allows it)

Reverse- 3.00

42FRE: More information on this tranny in time, it is matted with the 3.7 for our '04 models

4(2,4)RE Torqueflite: The 42RE is matted with the 3.9L, The 44RE is matted with 5.2L engines

1st- 2.74

2nd- 1.54

3rd- 1.00

4th- 0.69

Reverse- 2.21

46RE Torqueflite: This is matted strictly the 5.9L in our trucks. It is a similar construction to the other Torqueflites but as you can see there is a difference in gearing.

1st- 2.45

2nd- 1.45

3rd- 1.00

4th- 0.69

Reverse- 2.35

Aisin AX-15 Manual: Is the 5-speed transmission in I-4 model and supposedly early 6 cylinder models as well (someone verify that)

No data found

NV3500 Manual (MD): New Venture 3500 is the standard/stock manual transmission in our trucks

1st- 4.01

2nd- 2.32

3rd- 1.40

4th- 1.00

5th- 0.73

Reverse- 3.55

NV4500 Manual (L&HD): New Venture 4500 is a very awesome manual transmission that people may upgrade to truck

1st- 5.61

2nd- 3.04

3rd- 1.67

4th- 1.00

5th- 0.73

Reverse- 5.04

For those of us not great with numbers, I've type a paragraph or two. Traditionally dodge truck/suvs 4 and 5 speed automatic transmissions, have 3 normal gears and 4 & 5th are overdrive gears. The automatics have the lower normal and overdrive gears which is the reason they are more fuel efficient at cruising/highway speeds. The automatic transmissions do just that and are good for cruising around and long distance driving. But for the more truck stuff like towing and off-road they are in my opinion completely inadequate. Chrysler itself actually admits that the older Torqueflite transmissions matted with the 3.9 and 5.2L are not suited for heavy duty work as they were designed for light duty.

Now this is where the NV3500 comes in. The lower 1st gear gives significant advantages when towing, and 5th gear isn't so low that you can still use overdrive while towing in some situations. Plus not to mention every advantage from engine braking, holding gears and intuitive shifting. The standard version is rated with an input of 310 ft. lbs. of torque and has a GVWR is rated at 7,500 lbs. with a CGVWR of 11,000 lbs. As a note for those who are looking around for replacements or are just curious. Our trucks only use the wide gear ratio version of this tranny, not the narrow. No GM tranny version is like a Dodge, don't use them as a replacement, Ram 1500 and Dakota share the same gear ratios.

This is where the NV4500 manual transmission comes to the party. This 5 speed stick is perfect and at home in a truck, there can always be better things but this is great. Although the gearing is similar to the 545RFE, the NV4500 was created almost a decade before it. The LD version is designed with GVWR of 14,500 lbs. so in Dakotas and Durangos it is rated to handle 3,000 lbs more then what our GVWR rates us. 

Links (I do not vouch for their quality, they are an additional resource):

For rebuilding 42RE transmissions

For rebuilding 44RE transmissions

For rebuilding 46RE transmissions

Video for rebuilding NV3500 transmissions (google search, it keeps embedding the video) - personally I'd vote for just bolting up a NV4500 replacement

For rebuilding NV4500 transmissions - this is an HD version from a cummins but it is well documented

Please note that you should always use a manual when rebuilding transmissions, these links are to give visual examples and further assist you in rebuilding it. To put it simply the post writers and myself are not liable if you mess up.

This link http://dodgeforum.com/forum/1036359-post14.html , is information about how to understand improving your mpg with math and engineering. Not just add more power. For a lot of us, many have tried to find the "magic" efficiency rpm number. One of our members has done quite a bit of math and has brought some engineering to the table. Take a look at this, I found it very interesting to read. A quick facts for those who don't have the time. 4.7L engines cruising (at 70 mph) at less than 2114 rpm and 3.7L/5.7/5.9L at less than 2011 rpm are considered undergeared. I don't quite know how to explain this but undergeared means that the engine is operating before the engine rpm where it can adequately produce power. I hope this helps and that anyone that is trying to understand regearing. Thanks to Magnethead who did probably over an hour worth of math and typing, we have a great first hand example of this.

Quote:

Originally Posted by magnethead
NOTE: The following data is erroneous. My tires check out at 29.75", but for anybody on 4.10's with 32's, have at it.

I'm going to extend this a touch, just to see if Hank's numbers and my numbers match. Keep in mind I have the weakling 3.9.

Horsepower 175 hp @ 4400 rpm
Torque 230 ft. lbs. @ 3200 rpm
Bore x Stroke 3.91 x 3.31 in.

2175 rpm = 1200/(2x3.31/12)

4th gear with convertor locked up:
= (2175 / 0.69 / 4.10 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 768.82 * 0.0952
= 73 MPH

3rd gear with convertor locked up (tow/haul mode):
= (2175 / 1.00 / 4.10 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 530.48 * 0.0952
= 50.5 MPH

2nd gear with convertor unlocked (20% slip assumed)
= (2175 / 1.54 * 0.8 / 4.10 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 275.578 * 0.0952
= 26.23 MPH


Now lets go run back through that with the 3.55's and 30" tires my truck left the assembly plant with:

4th gear with convertor locked up:
= (2175 / 0.69 / 3.55 ) * (30" * 3.141591 / 12 * 60 / 5280)
= 887.93 * 0.08925
= 79.24 MPH

3rd gear with convertor locked up (tow/haul mode):
= (2175 / 1.00 / 3.55 ) * (30" * 3.141591 / 12 * 60 / 5280)
= 612.67 * 0.08925
= 54.68 MPH

2nd gear with convertor unlocked (20% slip assumed)
= (2175 / 1.54 * 0.8 / 3.55 ) * (30" * 3.141591 / 12 * 60 / 5280)
= 318.27 * 0.08925
= 28.40 MPH

So based on that, Chrysler likely felt it would be better to lug the motor with tall gearing and keep the throttle most of the way open. Basically, the ideal situation would be OD off at 55MPH, or OD on at 75 MPH, and pick whatever you want in between because it's a parabolic curve (actually probably closer to 3rd or 5th degree).

With the regear/bigger, I didn't really make the losses too great for either 55 or 75 MPH. 30 -> 32" = 6% loss and 3.55 -> 4.10 = 15% gain, so I really only gained 9% of torque.

This is why I say I wish they made 4.30's for our trucks. Since most of this section's trucks are on 31.5-32.5" tires, the 4.30 reallocates the entire system.

4th gear with convertor locked up:
= (2175 / 0.69 / 4.30 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 733 * 0.0952
= 69.78 MPH

3rd gear with convertor locked up (tow/haul mode):
= (2175 / 1.00 / 4.30 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 505.81 * 0.0952
= 48.15 MPH

2nd gear with convertor unlocked (20% slip assumed)
= (2175 / 1.54 * 0.8 / 4.30 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 262.76 * 0.0952
= 25 MPH


4.30's with a 32" tire moves the economy state to right there at 70 MPH, which is the actually traveled speed of most interstates. The trade off is a pretty steep loss at 55 MPH.

But that's okay. 4.30's don't exist for our axles.

4th gear with convertor locked up:
= (2175 / 0.69 / 4.56 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 691.26 * 0.0952
= 65.80 MPH

3rd gear with convertor locked up (tow/haul mode):
= (2175 / 1.00 / 4.56 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 476.97 * 0.0952
= 45.41 MPH

2nd gear with convertor unlocked (20% slip assumed)
= (2175 / 1.54 * 0.8 / 4.56 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 247.78 * 0.0952
= 23.58 MPH

Now we have some pretty big moves. 4th gear isn't so bad, but we just can't get close to a 55 MPH economy number.

One more time.

4th gear with convertor locked up:
= (2175 / 0.69 / 4.88 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 645.93 * 0.0952
= 61.50 MPH

3rd gear with convertor locked up (tow/haul mode):
= (2175 / 1.00 / 4.88 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 445.70 * 0.0952
= 42.43 MPH

2nd gear with convertor unlocked (20% slip assumed)
= (2175 / 1.54 * 0.8 / 4.88 ) * (32" * 3.141591 / 12 * 60 / 5280)
= 231.53 * 0.0952
= 22.04 MPH

Now we aren't anywhere close to an efficiency range.


Chrysler engineers win.

Thank you Magnethead for all the work it is appreciated, because of that I can slack a little and give a shorter version of my work. I have a 545RFE tranny with 3.55 gears (you can look up top to get the gears for if you'd like). I have worn tires that stand at 29.25", the A/T3 tires I'm looking at are 30.5". For the purpose of this 30.5" is my tire, this is larger for a 265/70/16 size tire. For the 4.7L with a stroke of 3.40", 1,200 ft/min is 2,118 rpm. With a final gear of 0.68 using the 545RFE tranny and a diff of 4.10. You have your magic number of 69-70 mph. So depending on vehicle set up, your rpms will vary. For those who are closer to stock, 4.10 is better. Still 4.30 would be perfect for those of us who want bigger tires.

For those that are interested in an rpm calculator, I found a very nice one online. Not perfect but quite accurate. http://www.catherineandken.co.uk/sti/tyres.html

I'll edit this post with more information as I remember it, people update it or ask for more. I hope it helps everyone.